Phosphorus Chemical Shift Tensors of Phosphole Derivatives Determined by 31P NMR Spectroscopy of Powder Samples

The results of a systematic solid-state 31P NMR study of 5-phenyldibenzophosphole, DBP, its chalcogenides, and some of its transition metal complexes are reported. Phosphorus chemical shift tensors have been obtained from 31P NMR spectra of stationary samples and of samples spinning about the magic angle. The spans of the phosphorus chemical shift tensors for DBP and its chalcogenides are comparable to those of the corresponding compounds of triphenylphosphine; however, the asymmetry of the tensors for the DBP series reflects the reduced local symmetry at phosphorus. For the complexes (DBP)M(CO)5 and cis-(DBP)2M(CO)4, where M is a group 6 transition metal (Cr, Mo, W), the most shielded component of the phosphorus shift tensor is found to be relatively independent of the metal or complex, δ33 = −41 ± 8 ppm, and is thought to lie along or close to the P−M bond axis direction. In contrast, δ11 and δ22 show considerable variation but decrease systematically on descending the group from Cr to W. Group 10 metal...